Biomonitoring Using Least Terns and Black Skimmers In the Northeastern United States

Abstract

Population sizes and reproductive success in colonies of least terns (Sterna antillarum) and black skimmers (Rynchops niger) were examined from Massachusetts to Cape May, New Jersey, to determine the utility of these species for monitoring population trends and environmental quality. Although some colonial species have been monitored for reproductive success, most schemes monitor only numbers of breeding birds or are more restricted geographically. For least terns in 1991 reproductive success was significantly lower on Long Island and higher in New Jersey. These differences persisted when compared with reference data from the previous 13-15 years for several of the same colonies that were relatively uncontaminated. There were no geographical differences in reproductive success in 1991 for black skimmers, although western Long island productivity was below normal. The differences in reproductive success coupled with stable population numbers suggest that southern New Jersey may be providing excess young least terns and black skimmers that move into parts of New York with low reproductive success. Monitoring population numbers alone may not be adequately sensitive for management. Monitoring of productivity though more labor intensive allows the early identification of problem regions and temporal trends. Regional monitoring of reproductive success may he essential to determining the relative importance of protecting specific colonies, and for the early recognition of human impacts.